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Watershed Academy Web |   |
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Wetland Functions and Values
Introduction Bill Sipple, USEPA Office of Water This module is about the benefits, or values, that wetlands provide. These values arise from the many ecological functions associated with wetlands. These societal benefits and ecological functions are discussed in detail below, and in some instances resource-specific or site-specific examples are presented. Much of the material was drawn from sources that are cited in the Acknowledgments, References, and World Wide Web Sources sections following the body of the text. Wetland functions and values discussed in this module appear in red, bold italics. Only relatively recently have we begun to understand the many ecological functions associated with wetlands and their significance to society. Wetlands were once considered useless, disease-ridden places (e.g., malaria and yellow fever) that were to be avoided. We now realize that wetlands provide many benefits to society -- such as fish and wildlife habitats, natural water quality improvement, flood storage, shoreline erosion protection, opportunities for recreation and aesthetic appreciation, and natural products for our use at little or no cost. Protecting wetlands can, in turn, protect our health and safety by reducing flood damage and preserving water quality. Wetlands are among the most productive ecosystems in the world, comparable to rain forests and coral reefs. They also are a source of substantial biodiversity in supporting numerous species from all of the major groups of organisms - from microbes to mammals. Physical and chemical features such as climate, topography (landscape shape), geology, nutrients, and hydrology (the quantity and movement of water) help to determine the plants and animals that inhabit various wetlands. Wetlands in Texas, North Carolina, and Alaska, for example, differ substantially from one another because of their varying physical and biotic nature. Wetland functions and values Wetlands can be thought of as "biological supermarkets." They produce great quantities of food that attract many animal species. The complex, dynamic feeding relationships among the organisms inhabiting wetland environments are referred to as food webs. The combination of shallow water, high levels of inorganic nutrients, and high rates of primary productivity (the synthesis of new plant biomass through photosynthesis) in many wetlands is ideal for the development of organisms that form the base of the food web -- for example, many species of insects, mollusks, and crustaceans (click for slide s02). Some animals consume the above-ground live vegetation (herbivore-carnivore food web); others utilize the dead plant leaves and stems, which break down in the water to form small, nutrient-enriched particles of organic material called detritus (click for slide s03). As the plant material continues to break down into smaller and smaller particles, it becomes increasingly enriched (nutritious) due to bacterial, fungal and protozoan activity. This enriched proteinaceous material, including the various microbes that colonize it, feeds many small aquatic invertebrates and small fish (click for slide s04). Many of these invertebrates and fish then serve as food for larger predatory amphibians, reptiles, fish, birds, and mammals (click for slide s05). Numerous species of birds and mammals rely on wetlands for food, water, and shelter, especially while migrating and breeding. Many animals need wetlands for part or all of their life-cycles. In late winter and early spring, for example, adult tiger salamanders migrate from uplands to vernal pools for breeding and egg deposition. The gilled larvae resulting from their fertilized eggs then develop further, eventually producing lungs. Therefore, they must leave the vernal pools for adjacent upland, generally forested, habitat as adults, where they are mainly subterranean. In this instance, a complex of wetlands within a forest matrix is important as the life-cycle requirements of the tiger salamanders change. Thus, for the existence of the tiger salamander, both wetlands and uplands are important and essential. This can similarly be said of other amphibians like the spotted salamander as well as many other animals. The diversity of habitats in a watershed (click for slide p01) or larger landscape unit is also important for other ecological functions associated with wetlands. One such function, biogeochemical cycling, involves the biologic, physical, and chemical transformations of various nutrients within the biota, soils, water, and air. Wetlands are very important in this regard, particularly relating to nitrogen, sulfur, and phosphorous. A good example of this occurs in anaerobic (non-oxygenated) and chemically reduced wetland soils and the muddy sediments of aquatic habitats like estuaries, lakes, and streams, which support microbes that function in nitrogen and sulfur cycling. Upon death and decay, the nitrogen and sulfur in plant and animal biomass is released through mineralization. Much of this is eventually transformed into gaseous forms and released into the atmosphere, where it once again becomes available to certain plants and their associated nitrogen-fixing bacteria in the soil. This is literally a major defense for mud, since it is the anaerobic and chemically reducing conditions in the substrate, in conjunction with various microbes, that ensure the gaseous release of the nitrogen and sulfur. On the other hand, phosphorous does not have a gaseous form, but vascular plants in wetlands transform inorganic forms of phosphorus (that might otherwise be shunted into undesirable algal blooms) into organic forms in their biomass as they grow. Thus, wetlands provide the conditions needed for the removal of both nitrogen and phosphorus from surface water. Scientists also point out that atmospheric maintenance is an additional wetland function. Wetlands store carbon within their live and preserved (peat) plant biomass instead of releasing it to the atmosphere as carbon dioxide, a greenhouse gas affecting global climates. Therefore, wetlands world-wide help to moderate global climatic conditions. On the other hand, filling, clearing and draining wetlands releases carbon dioxide. Wetlands also play an important role in the hydrologic cycle -- a cycle we all experience quite readily, for example, with the precipitation from a thunderstorm and the evaporation of ponded water from a puddle or bird bath. Wetlands can receive, store, and release water in various ways -- physically through ground water and surface water, as well as biologically through transpiration by vegetation -- and therefore function in this very important global cycle. Some specific examples of the benefits of wetlands to society are elaborated below. In addition, since wetlands play an integral role in the ecology of watersheds, two related Watershed Academy Web modules, Watershed Ecology and Wetlands and Watersheds (under development), are also pertinent. These additional modules will be very helpful in understanding the ecology of watersheds and the role of wetlands in a watershed context. Habitat for Fish, Wildlife, and Plants Fish and wildlife use wetlands to varying degrees depending upon the species involved. Some live only in wetlands for their entire lives; others require wetland habitat for at least part of their life cycle; still others use wetlands much less frequently, generally for feeding. In other words, for many species wetlands are primary habitats, meaning that these species depend on them for survival; for others, wetlands provide important seasonal habitats, where food, water, and cover are plentiful. For example, wetlands are essentially the permanent habitat of the beaver, muskrat, wood duck (click for slide s08), clapper rail, mud minnow, wild rice (click for slide s09) cattail, broadleaf arrowhead (click for slide s10) and swamp rose. For other species, such as largemouth bass, chain pickerel, woodcock, hooded warbler, otter (click for slide s11), black bear, raccoon, and meadow vole, wetlands provide important food, water, shelter, or nesting habitat. Numerous birds -- including certain shorebirds, wading birds (click for slide s12), and raptors, and many songbirds (click for slide s13) -- feed, nest, and/or raise their young in wetlands. Migratory waterfowl, including ducks, geese, and swans, use coastal and inland wetlands as resting, feeding, breeding, or nesting grounds for at least part of the year. For example, in the Chesapeake Bay Region (a major wintering area for waterfowl), coastal wetlands supported an annual average of nearly 79,000 wintering black ducks over a 45-year period (1950-1994); over the same period, it supported an annual average of about 14,000 wintering pintails. Most of these ducks rely on the prairie potholes (depressional wetlands) in upper mid-western United States and adjacent Canada and interior wetlands in northeastern North America for nesting. Indeed, an international agreement to protect wetlands of international importance was developed because some species of migratory birds are completely dependent on certain wetlands and would become extinct if those wetlands were destroyed (read on for the economic values associated with these resources.) The U.S. Fish and Wildlife Service estimates that up to 43% of the federally threatened and endangered species rely directly or indirectly on wetlands for their survival (e.g., the wood stork, Florida panther, whooping crane, swamp pink, and Canby's dropwort). Many others use wetlands at some point in their lives. Because they produce so much plant biomass and invertebrate life, estuaries and their coastal marshes serve as important nursery areas for the young of many game (recreational) and commercial fish and shellfish. Menhaden, flounder (click for slide s15), sea trout, spot, croaker, and striped bass are among the more familiar fish that depend on coastal wetlands. Such areas are also critical nursery habitat for young commercial shrimp along the Southeast and Gulf Coasts. Freshwater fish, such as the chain pickerel and northern pike (click for slide s16), use well-flooded or ponded wetlands as breeding and nursery areas. Some fish, like the brown bullhead and mud minnow, even subsist in wetlands that have natural low dissolved oxygen concentrations that unadapted species cannot endure. In the Pacific Northwest, some wetlands release cooler water to salmon-bearing streams and rivers; in places this is critical to the health of coldwater fish populations. Improving Water Quality and Hydrology Wetlands are valuable to us because they greatly influence the flow and quality of water. They help improve water quality, including that of drinking water, by intercepting surface runoff and removing or retaining inorganic nutrients, processing organic wastes, and reducing suspended sediments before they reach open water. For example, as the runoff water passes through wetlands, they retain or process excess nitrogen and phosphorus, decompose organic pollutants, and trap suspended sediments that would otherwise clog waterways and affect fish and amphibian egg development. In performing this filtering function, wetlands save us a great deal of money. A 1990 study showed that, the Congaree Bottomland Hardwood Swamp in South Carolina, removes a quantity of pollutants that would be equivalent to that removed annually by a $5 million waste water treatment plant. Another study at a 2,500 acre wetland in Georgia, indicated that it saves $1 million in water pollution abatement costs annually. Wetlands also reduce environmental problems, such as algal blooms, dead zones, and fish kills, that are generally associated with excess nutrient loadings. However, the capacity of wetlands to function this way is not unlimited, and too much surface runoff carrying sediments, nutrients, and other pollutants can degrade wetlands and thus the societal services they provide. In addition to improving water quality through filtering, some wetlands maintain stream flow during dry periods; others replenish groundwater. Many Americans, of course, depend on groundwater for drinking. The Floridian aquifer system, for instance, is one of the more productive ground water sources in the United States. It occurs across the entire state of Florida, and into southern Georgia, and portions of South Carolina and Alabama. This huge subsurface reservoir produces some of the cleanest water in the nation. Its primary source is rainwater that filters through hundreds of feet of sand and rock. One calculation for 5-acre Florida cypress swamp recharging groundwater was that, if 80 percent of swamp was drained, available ground water would be reduced by an estimated 45 percent. Flood Protection Because of their low topographic position relative to uplands (e.g., isolated depressions, floodplains), wetlands store and slowly release surface water, rain, snowmelt, groundwater and flood waters. Trees and other wetland vegetation also impede the movement of flood waters and distribute them more slowly over floodplains (click for slide 18b). This combined water storage and slowing action lowers flood heights and reduces erosion downstream and on adjacent lands. It also helps reduce floods and prevents waterlogging of agricultural lands. Wetlands within and downstream of urban areas are particularly valuable in this regard, counteracting the greatly increased rate and volume of surface-water runoff from pavement and buildings. Preserving and restoring wetlands, together with other water retention, can often provide the level of flood protection otherwise provided by expensive dredging operations and levees. The preservation of wetlands also results in many other benefits to society, such as the protection of ecologically significant fish and wildlife habitat. A good example of this is the Mississippi River's bottomland hardwood-riparian wetlands, which once stored at least 60 days of floodwater and represented significant fish and wildlife habitat. They now store only 12 days of floodwater because most have been filled, leveed, or drained, with substantial loss of fish and wildlife habitat. Another good example is Minnesota, where the cost of replacing the natural flood control function of 5000 acres of drained wetlands was found to be $1.5 million annually. (click for slide 18c) To quote Henry Wessman, the mayor of Grand Forks, ND: "The total cost of flood damage is born by taxpayers again and again as the flood waters come. I offer as a suggestion to compensate farmers within the area to actually retain natural wetlands. If you look at the costs of compensating farmers for such activities as opposed to the almost annual cost of flood protection and flood fighting within a city such as Grand Forks, you would realize that over the long haul, you are doing yourself a much greater service by retaining that water rather than by continually paying for flood damage." Therefore, in addition to their fish and wildlife values, wetlands reduce the likelihood of flood damage to homes, businesses, and crops in agricultural areas. They also help control increases in the rate and volume of runoff in urban areas. This protection results in less monetary flood damage (and related insurance costs), as well as protection of human health, safety, and welfare. Shoreline Erosion Because of their position on the landscape, wetlands at the margins of lakes, rivers, bays, and the ocean help protect shorelines and stream banks against erosion. Wetland plants hold the soil in place with their roots, absorb the energy of waves, and break up the flow of stream or river currents. The ability of wetlands to control erosion is so valuable that some states (e.g., Florida) are restoring wetlands in coastal areas to buffer the storm surges from hurricanes and tropical storms by dissipating wave energy before it impacts roads, houses, and other man-made structures. Economic Benefits of Wetland Resources We use many natural products from wetlands, including mammals and birds, fish and shellfish, and timber. For example, wetlands supporting timber totals about 55 million acres, two-thirds of which occurs east of the Rocky Mountains. Similarly, various plants like blueberries, cranberries, mints, and wild rice, are produced in wetlands. We also derive medicines from wetland soils and plants. Many of the nation's fishing and shellfishing industries harvest wetland-dependent species (e.g., striped bass and brown shrimp). In fact, the fish and shellfish that depend on wetlands for food or habitat constitute more than 75% of the commercial and 90% of the recreational harvest (click for slide s21). In the Southeast, fish and shellfish species dependent upon coastal and estuarine wetlands comprise almost all of the commercial catch. The coastal marshes of Louisiana alone produce a commercial fish and shellfish harvest amounting to 1.2 billion pounds annually, which was worth $244 million in 1991. In this region, 96% of the commercial harvest and more than 50% of the recreational catch are estuary-coastal wetland-dependent fish and shellfish. The United States commercial fisheries harvest is worth more than $2 billion annually. This harvest is the basis for a $26.8 billion fishery processing and sales industry. Overall, including commercial and recreational endeavors, seafood is a $50 billion industry. Wetlands are habitats for commercial fur-bearers like muskrat, beaver, otter, and mink, as well as reptiles such as alligators (click for slide s22). The nation's harvest of muskrat pelts alone valued at over $70 million annually, while the alligator industry is valued at $16 million. Recreation, Education, and Research Wetlands provide many recreational, educational, and research opportunities. In the United States, more than half of all the adults (98 million) hunt, fish, birdwatch or photograph wildlife, annually spending a total of $59.5 billion in the process (click for slide s24). Coastal areas themselves attract at least 100 million Americans each year. At least $18 billion in economic activity is generated annually from coastal wetland-dependent recreational fishing by 17 million Americans. Nature-related recreation is the fastest growing activity of the tourism industry - with an annual increase of about 30% since 1987. In 1996, 160 million Americans spent $29.2 billion to observe, photograph or feed wildlife. Much of this nature-based tourism involves birds, many of which are wetland-dependent. Each year, about $20 billion are spent on seed, travel and equipment by birders. Birding has increased more quickly than other outdoor recreation activities, such as biking, pleasure walking, skiing and golf. In fact, participation has tripled from 1982-83 (21 million) in to 1997 (63 million in 1997). The birding public is quite active - 24.7 million people took trips away from home to partake in birding, spending $5.2 billion in goods and services in 1991. This high level of participation by Americans in bird-related recreation is a clear indicator of the societal value of birds. An inordinate amount of this recreational birding is associated with wetlands and aquatic habitats. This undoubtedly relates to the fact that birds in particular tend to gravitate towards wetlands and aquatic habitats, which in turn attracts natural history and outdoor enthusiasts. Nationally, economic activity directly associated with non-consumptive enjoyment of birds generated 191,000 jobs and more than $895 million in sales and income tax revenues in 1991. In addition, 3 million migratory bird hunters generated $1.3 billion in retail sales, with a total economic multiplier effect of $3.9 billion, associated with 46,000 additional jobs and sales and income tax revenues of $176 million. Regional statistics on birding activity are also impressive. A prime example is the Delaware Bay shore and Cape May peninsula of New Jersey, which realizes more than $40 million annually from birders. In addition, artists and writers capture the beauty of wetlands on canvas and paper, or through cameras, and video and sound recorders. Others appreciate wetlands by hiking, boating, and other recreational activities. Almost everyone likes being on or near the water; part of the enjoyment is the varied, fascinating life forms (click for slide s26) found in these biologically rich areas. The recreational benefits associated with wetlands, of course, also serve to educate. Wetlands are studied in conjunction with environmental programs at adult continuing education facilities and at environmental centers. Furthermore, many school systems at the grammar, middle, and high school levels use these valuable ecosystems as out-of-door laboratories for environmentally-related courses, since they serve as excellent study sites to learn about vegetative structure (e.g., the density and cover of the vegetation) and ecological functions (e.g., nutrient cycling) , natural ecological processes (e.g., plant succession), biodiversity, and plant-animal interactions. For more advanced students, particularly those at the high school and college levels, and professionals seeking to learn more about wetlands, they serve as excellent research sites. Summary Wetlands provide many societal benefits: food and habitat for fish and wildlife, including threatened and endangered species; water quality improvement; flood storage; shoreline erosion control; economically beneficial natural products for human use; and opportunities for recreation, education, and research. Click on the buttons below to view a detailed list of functions and values and to check your retention by taking the self-test.
Acknowledgments The text of this module was derived, with substantial modifications and additions, from two EPA publications, America's Wetlands: Our Vital Link Between Land and Water (1995) and Wetlands Fact Sheets (1995). Other References and World Wide Web Sources utilized are given below. The author appreciates the review of drafts of this module by Rachel Doughty, John McShane, John Meagher, Tracie Nadeau, Douglas Norton, Sean Sipple, and Lynne Trulio. Appreciation is also expressed for the use of the following figures from America's Wetlands: Figures 1-27. Credits for original slides/illustrations are: slide s01(Mary Sharp), slide s02 (Bill Sipple), slide s03 (Bill Sipple), slide s04 (Joel Rogers), slide s05 (Bill Sipple), slide s06 (Matt Perry), slide s07 (Bill Sipple), slide s08 (Tim McCabe), slide s09 (unknown), slide s10 (unknown), slide s11 (Texas Parks and Wildlife Department), slide s12 (Herb Stein), slide s13 (Tom Blagden, Jr.), slide s14 (John Taylor), slide s15 (EPA Region VI), slide s16 (unknown), slide s17 (Todd Votteler), slide s18 (Bill Sipple), slide s19 (Kelly Drake), slide s20 (Steve Delaney), slide s21 (unknown), slide s22 (U.S. EPA), slide s23 (Texas Parks and Wildlife Department), slide s24 (unknown), slide s25 (Bill Sipple), slide s26 (Jennifer Matchett), slide s27 (Doug Norton). References Ewel, K. 1990. Multiple demands on wetlands; Florida cypress swamps can serve as a case study. Bioscience 40: 660-666. Feierabend, S.J. and J.M. Zelazny. 1987. Status Report on our Nation's Wetlands. National Wildlife Federation: Washington, DC. 50 pp. Lewis, R.R.1990. Creation and restoration of Coastal Plain wetlands in Florida. In: Kusler and Kentula (editors), Wetland creation and restoration: The status of the science. pp. 73-101. Mitsch, W.J. and J.G. Gosselink. 1993. Wetlands. 3rd Edition. Van Nostrand Reinhold: NY, NY. Office of Technology Assessment. 1993. Preparing for an uncertain Climate - Vol. II, OTA-O-568 Washington, DC: U.S. Government Printing Office, October, 1993. Perry, M.C. and A.S. Deller. 1994. Waterfowl population trends in the Chesapeake Bay area. Proceedings of the 1994 Chesapeake Research Conference. Toward a Sustainable Coastal Watershed: The Chesapeake Bay Experiment. June1-3, 1994. Norfolk, VA. pp. 490-504 Sipple, W.S. 1999. Days Afield: Exploring wetlands in the Chesapeake Bay Region. Gateway Press, Baltimore, MD. 558 pp. U.S. Environmental Protection Agency. 1994. National water quality inventory. 1992 Report to Congress. EPA 841-R-94-001. EPA: Washington, DC. U.S. Environmental Protection Agency. 1995a. Wetlands fact sheets. Office of Water, Office of Wetlands, Oceans and Watersheds. EPA843-F-95-001. U.S. Environmental Protection Agency. 1995b. America's wetlands: Our vital link between land and water. Office of Water, Office of Wetlands, Oceans and Watersheds. EPA843-K-95-001. World Wide Web Sources Manomet Center for Conservation Sciences. Western Hemisphere Shorebird Reserve Network. 1999. The North American bird conservation initiative in the United States: A vision of American bird conservation. (September 7, 1999 review draft). Retrieved December 5, 2000 from URL: http://www.manomet.org/USSCP/nabci-us.htm NOAA. National Oceanic and Atmospheric Administration 1995a. A $1.01 million project to restore wetlands in Louisiana to combat severe shoreline erosion. April 19, 1995. from URL: http://www.noaa.gov/ North Carolina State University. Values of wetlands. Retrieved December 5, 2000 from URL: http://h2osparc.wq.ncsu.edu/info/wetlands/values.html
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